Vitamin D2 vs D3: What’s the Difference & Which Supports Immunity Best?
, by Tatianna Gerard, 19 min reading time
Busy routines, indoor lifestyles, and sunscreen (as important as it is) can all make it harder to get enough vitamin D from the sun alone. That’s why more Australians are turning to supplements — but here’s something most people don’t realise: the type of vitamin D you take can affect how well it actually works.
There are two main forms: vitamin D2 and vitamin D3. Vitamin D2 and D3 both help prevent deficiency, but when it comes to supporting your immune system and maintaining healthy vitamin D levels, one has a clear advantage.
What is vitamin D2 and where does it come from?
Let’s start with the basics.
Vitamin D2, also known by its scientific name ergocalciferol, is one of the two main types of vitamin D used in supplements and fortified foods. It’s usually derived from plant sources — most commonly certain types of mushrooms — and is often the form added to foods like cereals, margarine, and plant-based milk alternatives.
You might also see D2 used in prescription vitamin D treatments, especially for people with very low vitamin D levels, as it’s been used medically for decades.
But here’s where it’s important to understand the difference.
Although D2 can raise vitamin D levels in the blood, it’s not as efficient as vitamin D3 when it comes to long-term effectiveness. That’s because your body doesn’t absorb or use D2 as easily — a process known as bioavailability (which simply refers to how well your body can take in and use a substance).
In short: D2 can help, especially in situations where a quick boost is needed — but it’s not the most reliable option for maintaining healthy vitamin D levels over time, especially if you're aiming to support your immune system on a daily basis.
How vitamin D3 differs from D2
Now let’s look at vitamin D3 — also known as cholecalciferol.
This is the form of vitamin D that your body naturally produces when your skin is exposed to sunlight. Specifically, UVB rays trigger a reaction in the skin that helps your body make D3, which is then converted by the liver and kidneys into the active form your body can use.
Because it’s the same type of vitamin D your body makes on its own, D3 is generally better absorbed and more effective than D2 when taken as a supplement. Vitamin D3 is more efficient at raising and maintaining healthy vitamin D levels over time — which is particularly important for supporting your immune system, bone health, and overall wellbeing.
When it comes to food sources, D3 is found mostly in animal-based products like:
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Oily fish (e.g. salmon, sardines, mackerel)
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Egg yolks
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Liver
- Fortified dairy products
Vitamin D3 supplements are typically made from lanolin, a natural substance found in sheep’s wool, though vegan-friendly D3 made from lichen is now becoming more widely available as well.
So, if you're looking for a supplement that works in line with how your body naturally produces and uses vitamin D, D3 is the closest match — and the most effective option for daily support.
D3 vs. D2
Now that we’ve looked at both forms individually, let’s compare vitamin D2 and D3 side by side.
While they’re both technically forms of vitamin D and help prevent deficiency, they’re not quite equal when it comes to how your body processes and benefits from them. The differences mainly come down to where they come from, how well they’re absorbed, and how long they stay active in your system.
Here’s a simple breakdown to make the comparison easier:
| Factor | Vitamin D2 (Ergocalciferol) | Vitamin D3 (Cholecalciferol) |
| Source | Plant-based (mushrooms, fortified foods) | Animal-based (lanolin, oily fish) or sunlight exposure |
| How it's made | Synthetic or derived from UV-exposed fungi | Naturally made in human skin from sunlight |
| Absorption (bioavailability) | Less efficiently absorbed and used by the body | More easily absorbed and longer-lasting in the body |
| Potency | Weaker at raising long-term vitamin D levels | Stronger and more effective at maintaining optimal levels |
| Stability | Breaks down more quickly when stored or exposed to light | More stable and longer-lasting in supplements |
| Supplement use | Sometimes used in prescriptions or fortified plant foods | Common in over-the-counter supplements and health products |
So, what does this all mean for you?
If your goal is to maintain healthy vitamin D levels, support your immune system, or just get the most benefit from your supplement, vitamin D3 is generally the more effective choice. It mimics the way your body naturally produces vitamin D and stays active in your system for longer — making it a better fit for long-term support.
That’s not to say D2 doesn’t have its place. In some situations (like prescription treatments or plant-based diets), it may still be used. But for most people, especially those choosing a supplement for daily immune or wellbeing support, D3 is the clear winner.
Why vitamin D3 is better for immune support
When it comes to immune health, vitamin D3 stands out as the superior form of vitamin D — and the reasons go beyond just absorption.
D3 is more efficient at raising and maintaining vitamin D levels
Your immune system depends on a steady, healthy level of vitamin D to do its job — from fighting off viruses and bacteria to helping control inflammation. Studies have consistently shown that vitamin D3 is more efficient than D2 at increasing blood levels of vitamin D (known as serum 25(OH)D) and keeping them stable over time.
In other words, D3 gives your body a more reliable supply of what it needs to keep your defences strong, especially during winter months or if you're spending more time indoors.
D3 mimics the natural form your body makes from sunlight
Vitamin D3 (cholecalciferol) is the same form your body produces when your skin is exposed to sunlight. Because of this, it fits more naturally into your body’s biological processes. It’s better recognised, more easily absorbed, and stays in circulation longer than D2.
This is important when you consider how the immune system works. Immune cells like T-cells and macrophages have vitamin D receptors, which means they respond directly to vitamin D signals — but only if there's enough of it available, and in a usable form like D3.
Vitamin D supports both innate and adaptive immunity
Vitamin D isn’t just a general wellness nutrient — it plays a direct role in regulating immune responses. It supports two key parts of the immune system:
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Innate immunity: Your body’s first line of defence, which helps fight off unfamiliar invaders like bacteria and viruses. Vitamin D enhances the activity of antimicrobial peptides — natural substances that destroy germs before they can cause illness.
- Adaptive immunity: This is your more targeted defence system. Vitamin D helps prevent overreactions from the immune system (which can lead to excessive inflammation), while also supporting proper antibody production to help your body remember and respond to threats more effectively.
Because D3 raises vitamin D levels more effectively than D2, it’s better at supporting both sides of this immune balance.
D3 may offer added protection against respiratory illness
Several studies and reviews have linked vitamin D supplementation — particularly D3 — with reduced risk of respiratory infections, including colds, flu, and even complications from more serious viruses. While no supplement can replace medical treatment or guarantee prevention, research suggests that people with higher levels of vitamin D are less likely to get seriously ill from common respiratory infections.
This is especially relevant for older adults, people with asthma or chronic lung conditions, or anyone with limited sun exposure.
D3 is better for long-term health and maintenance
Since D3 is more potent and lasts longer in the body, it’s better suited for daily or ongoing support — especially if you’re taking vitamin D as part of a long-term immune or wellness routine. This means your levels stay more consistent over time, and you may not need to take it as frequently to maintain the benefits.
Research shows that vitamin D3 is significantly more effective at raising and sustaining blood levels of vitamin D than D2. It's estimated that D3 is around 87% more potent in increasing and maintaining serum 25(OH)D levels — which is the main marker used to measure vitamin D in the body. It also results in two to three times greater storage of vitamin D compared to an equivalent dose of D2.
By contrast, D2 tends to break down more quickly in the body, meaning it may require higher or more frequent dosing just to achieve similar results — and it may not offer the same steady support over time.
When might vitamin D2 be used?
While vitamin D3 is generally the preferred form for boosting and maintaining healthy vitamin D levels, vitamin D2 still has a place — particularly in certain medical or dietary situations.
Here are a few examples of when vitamin D2 might be used:
1. When prescribed by a doctor
Vitamin D2 (ergocalciferol) is sometimes used in prescription-strength vitamin D treatments, especially for people with very low levels of vitamin D or those who need a short-term boost. In these cases, a healthcare provider may recommend D2 in high doses to quickly raise blood levels — often as part of a structured treatment plan.
2. For individuals following a strict plant-based or vegan diet
Because vitamin D2 is derived from plant sources, such as UV-exposed mushrooms or yeast, it’s often the form found in vegan-friendly supplements and fortified plant-based foods (like non-dairy milks and cereals).
That said, it’s worth noting that vegan-friendly D3 (usually sourced from lichen) is now becoming more widely available — and offers the same superior absorption and effectiveness as traditional D3 from animal sources.
Which supplement should you go for?
Now that you know the difference between vitamin D2 and D3, the next step is figuring out which supplement best fits your lifestyle and health goals.
You don’t need a medical degree to make a smart choice — just a few simple tips can help you read labels more confidently and pick a product that delivers real benefits.
1. Look for “cholecalciferol” on the label
When shopping for vitamin D supplements, check the ingredients for cholecalciferol — that’s the scientific name for vitamin D3. It’s the form that most closely matches what your body produces from sunlight and is more effective at raising and maintaining healthy levels over time.
2. Choose the right dose for your needs
Vitamin D supplements come in a range of strengths, from lower daily maintenance doses to higher short-term doses used to correct deficiencies. Finding the right one for you depends on factors like your age, skin colour, sun exposure, diet, and overall health.
As a general guide:
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Adults who get some sun exposure but not at the recommended level may need at least 600 IU per day, while adults over 70 are advised to aim for 800 IU per day.
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People who avoid sun exposure or are at higher risk of deficiency may require 1,000 to 2,000 IU daily.
- In cases of moderate to severe deficiency, healthcare professionals may recommend 3,000 to 4,000 IU per day for a limited period (6–12 weeks), followed by a maintenance dose of 1,000 to 2,000 IU per day to keep levels steady.
These recommendations are based on guidance from Healthy Bones Australia and are designed as a general framework — but it’s important to remember that vitamin D needs can vary from person to person.
If you're unsure of your current vitamin D status, it’s best to get a blood test and speak with your GP or pharmacist before starting a supplement — especially if you're considering higher doses. They can help you determine what’s right for your body and avoid over-supplementation.
For most healthy adults simply looking to support their immune system, a moderate daily dose of vitamin D3 (such as 1,000 IU) is usually a safe and effective option.
3. Consider your lifestyle and diet
When it comes to choosing the right vitamin D supplement, your everyday habits play a big role in how much your body naturally produces — and how much support you might need through your diet or supplements.
Here are a few things to think about:
How much sun are you getting?
Your body creates vitamin D3 when your skin is exposed to direct sunlight — specifically UVB rays. But depending on the season, time of day, where you live, and even how much skin is uncovered, this process can vary a lot.
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If you spend most of your time indoors, work night shifts, or cover up with clothing or sunscreen (which is important for skin protection), you may not be making enough vitamin D on your own.
- In Australia, sun exposure during the cooler months or in southern states may not be strong enough to support adequate vitamin D production, especially for older adults.
Is your diet giving you enough vitamin D?
Very few foods naturally contain vitamin D, and most of them are animal-based.
Some examples include:
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Oily fish like salmon, sardines, and mackerel
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Egg yolks
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Liver
- Fortified products like cow’s milk, margarine, or cereals
If your diet doesn’t include these foods regularly — or if you follow a vegetarian or vegan lifestyle — you may need to consider a supplement to fill the gap.
Are you choosing plant-based options?
If you're following a vegan or plant-based diet, it's important to check the label of your supplement.
Do you regularly use sunscreen or wear covering clothing outdoors?
Sun safety is essential — especially in Australia where UV levels can be extreme — but it also reduces the skin’s ability to synthesise vitamin D. If you're someone who’s diligent with sun protection (as you should be), a supplement may help balance that out.
Are you in a higher-risk group?
Certain groups are more likely to have low vitamin D levels, including:
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Adults over 70
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People with darker skin tones (which naturally filters more UVB)
- People with certain medical conditions that affect absorption (e.g., coeliac or kidney disease)
4. Quality matters
Not all supplements are made to the same standard, so it’s worth choosing a brand you can trust — especially when it comes to something as important as long-term immune and bone health.
Look for supplements that are:
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Made by reputable manufacturers
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Clearly labelled with dosage and ingredients
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Free from unnecessary fillers or artificial additives
- Backed by third-party testing
There are plenty of high-quality Australian brands that consistently meet these standards, including:
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Australian Natural Care (ANC)
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Blackmores
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Swisse
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Ethical Nutrients
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BioCeuticals
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Herbs of Gold
- Fusion Health
These brands are known for their commitment to quality, science-backed formulations, and using ingredients your body can absorb and use effectively.
At Aussie Pharma Direct, we stock Australian Natural Care — a trusted homegrown brand with a long-standing reputation for premium-quality supplements.
If you’re looking to support your immune system or bone strength, take a look at:
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Vitamin D3 1000 IU Supplement – a simple, effective daily D3 dose
- Calcium + Vitamin D3 & K2 Supplement – great for those looking to support both bone and heart health
Conclusion
It’s easy to overlook the fine print when buying a supplement, but in the case of vitamin D, knowing the difference between D2 and D3 really does matter.
Understanding the difference between vitamin D2 and D3 gives you the power to choose the form that works with your body, not just for it. With vitamin D3, you're giving your immune system and overall wellbeing the consistent, reliable support it needs.
And if you’re unsure about your current vitamin D levels, it’s worth considering a simple blood test. These days, you don’t even need to book a pathology visit — the TouchBio Vitamin D Rapid Test Kit allows you to check your vitamin D status from the comfort of your home with just a small finger prick. It's quick, fuss-free, and ideal for anyone keeping an eye on their levels — especially if you’re managing a condition or taking supplements regularly.
For those monitoring on an ongoing basis, keeping a few test kits on hand means you can stay in control without needing to visit a clinic each time.
Sometimes, the smartest health decisions come from simply knowing where you stand — and making sure the support you're giving your body is actually what it needs.
